Twelve Mile Circle decided to stick with the aqueduct theme once again after the recent discussion of England’s Barton Swing Aqueduct. There were other structures, equally fascinating in their own distinct ways. Some were large, some were unusual, and some offered elements of both. Many of those innovative structures seemed to concentrate in western Europe, an obvious leader in navigable inland waterways.
Aqueducts designed simply to move water were interesting by themselves, however I was considerably more fascinating by those designed to carry boat traffic above the surrounding terrain, akin to a bridge for boats for a lack of better words. For more than a century the title of longest navigable aqueduct had been held by the Briare aqueduct of the Canal latéral à la Loire, the canal over the Loire River in France (map). It was a magnificent masonry structure with a steel trough stretching 662 metres (0.4 miles). Then came Germany’s Kanalbrücke Magdeburg, or Magdeburg Water Bridge in 2003 (map), considerably longer at 918 metres (0.6 miles) albeit more utilitarian than beautiful.
In what’s being hailed as an engineering masterpiece, two important German shipping canals have been joined by a giant kilometer-long concrete bathtub… The water bridge will enable river barges to avoid a lengthy and sometimes unreliable passage along the Elbe. Shipping can often come to a halt on the stretch if the river’s water mark falls to unacceptably low levels.
The Magdeburg Water Bridge provided a vital direct connection between two separate canals on either side of the River Elbe, the Mittellandkanal and the Elbe-Havel, essentially connecting eastern and western Germany directly by water as well as to nations beyond its borders from Poland to France and the Benelux region. The possibility had been envisioned at the turn of the last century when construction first began. Two World Wars and the politics of a protracted Cold War completely halted the dream. German reunification provided an impetus to renew and complete this effort, nearly a century after initial construction first began. Now it’s a reality.
Belgium’s Port of Antwerp locked-up (pun alert) the title for the world’s largest canal lock. It handled 200 million tonnes of cargo in 2015, enough to make Antwerp one of the Top 20 busiest ports in the world, and it "aims to keep growing," Locks were necessary to protect the port from strong tidal actions pushing in and out along the Scheldt River. The locks kept water levels constant on the port side of the structures. Oceangoing cargo container ships kept growing larger so the locks had to follow suit in a continual game of catch-up. They became truly mammoth.
Antwerp first claimed the largest lock title with the construction of the Zandvlietsluis, or Zandvliet Lock, in 1967. That remained sufficient for a solid three decades until a new class of larger ships threatened to diminish the port’s usefulness. The port authority responded by opening a new lock parallel to the Zandvlietsluis in 1989, the Berendrechtsluis, or Berendrecht Lock. It was great enough to accommodate Post Panamax container ships (Panamax being an official set of dimensions for the largest ships that can navigate the Panama Canal). The Berendrecht Lock, currently the largest lock in the world, is 68 metres (223 ft) wide, about 11 metres (36 ft) wider than the Zandvliet Lock.
Right on schedule, however, container ships grew once again to an even larger behemoth class called New Panamax. Elsewhere in the Port of Antwerp, engineers are building the Deurganckdoksluis, or the Deurganckdok Lock. It will encompass the same length and width as Berendrecht, and in addition it will be four metres deeper to accommodate the extra draft of New Panamax ships. The Deurganckdok Lock was undergoing testing at the time I posted this article and was expected to open in April 2016.
Obviously Twelve Mile Circle fixated on superlatives like the world’s longest navigable aqueduct and the world’s largest lock, although the real reason for this article centered on a combination of the two: the worlds longest/largest aqueduct with a built-in lock. Actually there was but a single example of such an unusual structure currently, the Netherlands’ Naviduct. The concept was so new that the term stood on its own. THE Naviduct.
The whole situation seemed odd. The Netherlands was renowned for land reclamation and that figured indirectly into the creation of the Naviduct. The nation planned to drain a 410 km2 (158 mi2) polder — about the size of the Caribbean island of Barbados — to be called Markerwaard. It went so far as to create a 27 km (17 mi) dike between Enkhuizen and Lelystad that it completed in 1975 and called the Houtribdijk, resulting in two large lakes, Markermeer and IJsselmeer. However the project stalled and the Netherlands abandoned its plan altogether a couple of decades later. Nonetheless the nation still had a long dike which, by that time, carried the new N302 Motorway that separated two large lakes. Authorities also built a lock between the two lakes, a necessary step because prevailing winds affected the lakes differently even though they were at the same elevation. However ships and cars couldn’t cross the point at the same time. It created a transportation mess.
Thus, Dutch officials faces simultaneous dilemmas of their own creation: a problematic connection between two bodies of water; and a transportation bottleneck impacting maritime and automotive traffic. They responded by designing an aqueduct with a lock built within it, the Naviduct. Motorway traffic flowed below the aqueduct while ships sailed across it. I don’t know why they didn’t simply build either a tunnel or a bridge for the motorway. Regardless, their preferred solution was infinitely more interesting and it went into service in 2003. The structure remains the only Naviduct for the time being although it has been considered as a possible solution for other locations in the Netherlands. It would be hard to imagine its usefulness elsewhere since few other places face the same set of extreme geographic challenges. We should simply enjoy its existence.
England underwent an extensive Canal Age in the mid Eighteenth Century, lasting for longer than a century. Waterways provided a cheaper means to move goods across a nation, helping to spark the country’s rapid transformation during the Industrial Revolution. Canals offered remarkable improvements over rutted, muddy overland routes and provided the best transportation alternative in the decades before the invention of railroads.
The Bridgewater Canal was frequently cited as the blueprint for a network that quickly evolved across the nation after it opened in 1761. Its builder and owner, Francis Egerton the third Duke of Bridgewater, envisioned a canal as a better way to move coal from his mines at Worsley to nearby towns. Coal from his mines heated homes and fueled industrial expansion. Egerton’s design hadn’t been tried in England before; his was the first canal that didn’t following an existing waterway. He kept his design simple. The canal followed natural topography so it didn’t require locks anywhere along its 65 kilometre (39 mile) path from Leigh to Runcorn; near Liverpool and Manchester. It was a narrow canal designed for small slender boats and it served its purpose well enough to inspire numerable imitators.
The Manchester Ship Canal, by contrast, was one of the last canals built and it didn’t arrive on the scene until the 1880’s. It traced the original paths of the rivers Mersey and Irwell, in a general manner. Industrialists in Manchester felt that they were at a disadvantage because of the city’s inland location inaccessible to oceangoing vessels. Manchester businesses paid dearly for railroad access to the docks at Liverpool. The city lobbied for relief and Parliament approved construction despite Liverpool’s strong objections. Construction required an immense effort with extensive dredging, numerous locks, and high overhead bridges to accommodate the passage of large cargo ships. These improvements allowed merchant vessels to sail all the way into Manchester and the city became an important seaport.
Where the Canals Crossed
That was all fascinating although the stories of two specific two canals didn’t differ materially from many of the dozens of other English canals. However the two canals crossed physical paths and that was where things got interesting. Engineers had to find a unique solution to accommodate the situation. The Bridgewater Canal, being the older structure, crossed above the River Irwell on an historic stone arched aqueduct at the town of Barton-on-Irwell. Oceangoing ships on the new Manchester Canal, following the path of the River Irwell, would never be able to fit beneath the aqueduct. It had to be demolished. In its place rose a marvelous manifestation of Victorian design, a swing aqueduct.
The Barton Swing Aqueduct became the first and possibly the only structure of its type anywhere in the world. It was designed to pivot 90 degrees whenever large ships traveling along the Manchester Canal approached it, allowing them to pass without obstruction. Engineers created an artificial island at the center of the canal that served as the pivot point. A control tower built on the island contained the necessary machinery to operate the swing. Some of process involved manual labor as evidenced by the YouTube video. One can see a worker operating a hand crank to move the watergate at the end of the aqueduct. The swing aqueduct is still in operation serving its original purpose, an engineering marvel.
In addition there was a road that crossed the Manchester Canal near the same point. It also required a swinging mechanism, and was called the Barton Road Swing Bridge. The same concrete island and control tower pivoted the road bridge at the same time it pivoted the aqueduct.
Reader "Qadgop the Mercotan" sent an email message to 12MC recently, referencing a conversation on the Straight Dope Message Board under the intriguing title, "Are there any streets with names containing all four cardinal points?" One of the participants on that board, kunilou, discovered a street that met the criteria: Southeast Circle NW in Albuquerque, New Mexico. And it appeared to run into Northeast Circle SW! (map). Many thanks to Qadgop the Mercotan for passing that along.
I thought I’d lump another set of somewhat related items together as I continued to cull the enormous backlog of possible Twelve Mile Circle topics. They didn’t have much in common except that they all involved continental Africa. Two were geographical observations and two were geological oddities. All of them piqued my interest although not enough to devote an entire article to them.
Most of us have probably seen the recent comparison-style maps on the Intertubes lately, some demonstrating Africa’s immense size. Brilliant Maps, for example, had a wonderful portrayal of the True Size of Africa in an article a few months ago. People tended to misconstrue Africa’s enormity, probably due to its under-representation in popular media combined with Mercator map projections that distorted its actual size. Twelve Mile Circle fell into some of those same traps as witnessed by the relatively few African article markers on the Complete Index page.
In that vein, I pondered Africa’s enormity in a slightly different manner using great-circle distances. And what better measure of great-circle distance could I generate than airline flights? One could take a direct nonstop flight from Lagos, Nigeria to Nairobi, Kenya (currently 7 flights per week on Kenya Airlines) and ponder its width. That would carry a traveler from west to east across the continent, not even its widest part, and it would take 5 hours and 20 minutes. That compared pretty nicely with a flight from New York to San Francisco across the width of the United States; or from London, England to Ankara, Turkey.
Looking at length, one could then take a nonstop flight from O. R. Tambo International Airport in Johannesburg, South Africa to Cairo, Egypt (4 flights per week on EgyptAir) in 8 hours, or alternately to Dakar, Senegal (3 flights per week on South African Airways) in 8.5 hours. That compared rather favorably with a flight between Chicago, Illinois and Paris, France. Of course, an entire ocean didn’t have to be crossed on any of those African flights. That, to me, demonstrated its vast expanse quite succinctly.
Plus, now I get to see all sorts of interesting advertisements on my website now that Big Data thinks I’m contemplating so many far-flung adventures.
Extreme Elevation (or Lack Thereof)
Gambie by Guillaume Colin & Pauline Penot on Flickr (cc)
Africa demonstrated many extremes, although not in every instance. Certainly a landmass of its size featured an array of elevations, from Mount Kilimanjaro in Tanzania (5,895 metres / 19,341 feet) down to Lake Assal in Djibouti (-153 m / -502 ft). I wondered though, which African nation had the smallest elevation extremes. I discounted the various offshore islands that were considered part of Africa and focused on the continent itself. The honor went to The Gambia. I featured Unusual Geography of the Republic of The Gambia in the very early days of 12MC and even commented on its elevation. What I didn’t note at the time was that its greatest "peak" (53 m / 174 f) was also the lowest national highpoint on the continent.
The website Peakbagger included this highpoint in its database, a place called Red Rock (map). Only one Peakbagger member claimed to have conquered its summit. I wasn’t surprised.
The continent also served as a home for what National Geographic dubbed the Strangest Volcano on Earth. The Ol Doinyo Lengai stratovolcano in the Gregory Rift of the larger East African Rift of Tanzania (map) was well known to vulcanologists for its unique properties. It was the only active volcano that was known to produce natrocarbonatite lava. The lava at Ol Doinyo Lengai wasn’t based on silica as was typical, rather it was composed of sodium and potassium carbonate minerals.
…the temperatures of these lavas are much lower, "only" about 600 deg. C., and Lengai’s lava does not emit enough light to glow during day,- only at night, a dull reddish glow that does not illuminate anything is visible. Also because of its peculiar chemical composition, the lava is extremely fluid and behaves very much like water, with the exception that it is black like oil. After it is cooled down it quickly alters and becomes a whitish powder.
Black water lava? I’d love to see some of that in person. I may have to settle for the YouTube video for now.
In the distant ancient history of the planet, something like two billion years ago, an asteroid slammed into the earth leaving an impact crater 300 kilometres (185 miles) across. The asteroid was much smaller than that, maybe 5-10 km in diameter, although it hit with such tremendous speed and force that it vaporized stone for great distances in all directions. This celestial divot was called the Vredefort crater — named for the South African settlement that grew there in modern times — the largest verified crater on the planet.
Very few signs remained because of its ancient pedigree, leaving it mostly eroded. A structure known as the Vredefort Dome sprouted at impact, an uplifting of rock that occurred at the very center of the strike. It was mostly weathered away too although it still appeared as a faint semi-circle on satellite images. A few roads also crossed its ridges, making it an interesting sight in Google Street View (image).
The thought of an impact that large seemed terrifying.